1 - INTRODUCTION
Congratulations! You have purchased a Jewell Instruments Miniature Tilt Sensor - the most precise
and repeatable commercial sensor for measuring gravity-referenced angular movements.
Your Miniature Tilt Sensor contains either one or two electrolytic tilt transducers, one for each
orthogonal axis of rotation. Series 755 sensors contain high-gain (Type A) transducers that resolve
angular changes smaller than 0.1 microradian over ±1 degree of arc. Series 756 sensors incorporate mid-
range (Type B) transducers that resolve 1 microradian over ±10 degrees. The type of transducers in your
Miniature Tilt Sensor is shown in Appendix B.
We recommend that your sensor be operated with signal conditioning electronics supplied by Jewell
Instruments LLC (Figure 1). It also may be operated using third-party electronics that supply appropriate
transducer excitation and signal conditioning of transducer output. Signal conditioning is discussed in
Section 3.0 of this manual.
Miniature Tilt Sensors are part of a family of precision instrumentation from Jewell Instruments LLC.
Included are 800 Series Uniaxial Tiltmeters, 700 Series Biaxial Tiltmeters, 500 Series Geodetic Tiltmeters,
and the new Electrolevel monitoring system. Jewell Instruments' instrumentation is used worldwide for
measuring the the behavior of dams, power plants, machinery, mines, bridges, buildings, tunnels, tanks,
retaining walls, wells, landslides, volcanoes, and other natural and manmade structures. Low-cost,
automated data acquisition and alarm systems are also part of Jewell Instruments' instrumentation family.
Please contact the factory for more information on these products.
2 - MECHANICAL DESCRIPTION
Series 755 and 756 Miniature Tilt Sensors are supplied in five standard sensor housings (Figures 2
and 3). In addition, special housing shapes, sizes, and materials are available upon customer request.
Standard housings are made of anodized aluminum. Housings also are available in stainless steel,
and invar for a small additional charge. The tilt transducers are potted into the housings with a special
ceramic cement.
Sensor housings are either single or dual axis, as indicated in Tables 1 and 2. Temperature sensors
are potted into several, but not all of the standard housings (Tables 1 and 2). Mounting holes allow for
easy attachment to almost any flat surface.
3 - ELECTRONIC SIGNAL CONDITIONNG
Your Miniature Tilt Sensor uses either one or two electrolytic tilt transducers as the sensing elements.
These transducers are essentially electronic spirit levels (electrolevels). They consist of a fluid-filled glass
vial with three electrodes mounted inside, in contact with the conductive fluid (Figure 4). The transducers
operate on the fundamental principle that a bubble, suspended in a liquid-filled case, is always bisected by
the vertical gravity vector. As the transducer tilts, the vial moves around the bubble, alternately covering
and uncovering the two excitation electrodes.
When a constant AC voltage is applied across the two excitation electrodes, the AC output measured
at the central pick-up electrode changes in linear proportion to the tilt angle. In other words, the transducer
behaves as an AC variable resistor (potentiometer). DC excitation may not be used to operate the
transducers. With suitable signal conditioning, the transducers in your Miniature Tilt Sensor will achieve
the performance specifications listed in the "Specifications" section of this manual.
